Electrically-tunable optical filter

ABSTRACT

An optical device stack includes at least one of a photodetector or an optical emitter and a metasurface. The metasurface is disposed over a light-receiving surface of the photodetector or a light emission surface of the optical emitter. The metasurface includes a first conductive layer having an electrically-tunable optical property and an array of conductive nanostructures disposed on a first side of the first conductive layer. A second conductive layer is disposed on a second side of the first conductive layer. An electrical insulator is disposed between the first conductive layer and the second conductive layer. A change in an electrical bias between the metasurface and the second conductive layer, from a first electrical bias to a second electrical bias, tunes the electrically-tunable optical property from a first state to a second state, and changes an electrically-tunable optical filtering property of the metasurface.

FIELD

The described embodiments relate generally to optical filters, such ascolor filters. More particularly, the described embodiments relate tooptical filters for optical sensors (e.g., ambient light sensors orproximity sensors) or optical emitters (e.g., flood or spotilluminators).

BACKGROUND

When sensing electromagnetic radiation, it may be necessary or useful tosense the intensity of different electromagnetic radiation wavelengths,or different ranges of electromagnetic radiation wavelengths. Typically,different electromagnetic radiation wavelengths or ranges are sensed bydifferent optical sensors, with the electromagnetic radiation receivedby different optical sensors being filtered by different optical filters(e.g., different color filters) positioned in the optical receptionpaths of different optical sensors.

It may also be necessary or useful to emit different electromagneticradiation wavelengths, or different ranges of electromagnetic radiationwavelengths, at different times. Typically, the differentelectromagnetic radiation wavelengths or ranges are emitted by differentoptical emitters, with different optical emitters being filtered bydifferent optical filters (e.g., different color filters) positioned inthe optical emission paths of the different optical emitters.

SUMMARY

Embodiments of the systems, devices, methods, and apparatus described inthe present disclosure are directed to optical sensors includingelectrically-tunable optical filters in their optical reception paths,and optical emitters including electrically-tunable optical filters intheir optical emission paths.

In a first aspect, the present disclosure describes an optical devicestack. The optical stack may include at least one of a photodetector oran optical emitter. A metasurface may be disposed over at least one of alight-receiving surface of the photodetector or a light emission surfaceof the optical emitter. The metasurface may include a first conductivelayer having an electrically-tunable optical property and an array ofconductive nanostructures disposed on a first side of the firstconductive layer. The optical stack may further include a secondconductive layer on a second side of the first conductive layer and anelectrical insulator disposed between the first conductive layer and thesecond conductive layer. A change in an electrical bias between themetasurface and the second conductive layer, from a first electricalbias to a second electrical bias, may tune the electrically-tunableoptical property from a first state to a second state and change anelectrically-tunable optical filtering property of the metasurface.

In another aspect, the present disclosure describes an optoelectronicdevice. The optoelectronic device may include a pixel, which in turnincludes a metasurface. The metasurface may include an array of goldnanowires disposed on a layer of indium tin oxide (ITO). The pixel mayalso include a layer of gold and a layer of alumina disposed between themetasurface and the layer of gold. A voltage source may be electricallyconnected to the metasurface and the layer of gold. A controller may beconfigured to change a voltage between the metasurface and the layer ofgold by programming the voltage source.

In still another aspect of the disclosure, the present disclosuredescribes a method of characterizing ambient light. The method mayinclude receiving a first set of wavelengths of the ambient lightthrough a metasurface while the metasurface is in a first state. Themetasurface may include an array of nanowires formed on a layer ofmaterial having an electrically-tunable optical property. The method mayalso include measuring a first intensity of the first set ofwavelengths; applying a voltage to the metasurface to bias themetasurface to a second state different from the first state; receivinga second set of wavelengths of the ambient light through the metasurfacewhile the metasurface is in the second state; measuring a secondintensity of the second set of wavelengths; and characterizing theambient light using at least the first intensity and the secondintensity.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 shows an isometric view of a first example optoelectronic device;

FIG. 2 shows an isometric view of a second example optoelectronicdevice;

FIG. 3A shows an elevation of an example pixel of an optoelectronicdevice;

FIG. 3B shows a plan view of an example array of conductivenanostructures included in the pixel described with reference to FIG.3A;

FIG. 3C shows an isometric view of an example conductive nanostructureincluded in the array of conductive nanostructures described withreference to FIG. 3A or 3B;

FIG. 3D shows an alternative view of the layers circumscribed by thebubble IIID in

FIG. 3A;

FIG. 4 shows a graph of the different optical responses that may beprovided by a metasurface tuned to different representative states;

FIGS. 5A and 5B show a first example of an electronic device;

FIGS. 6A and 6B show a second example of an electronic device;

FIG. 7 shows an example block diagram of an electronic device; and

FIG. 8 shows an example method of characterizing ambient light.

The use of cross-hatching or shading in the accompanying figures isgenerally provided to clarify the boundaries between adjacent elementsand also to facilitate legibility of the figures. Accordingly, neitherthe presence nor the absence of cross-hatching or shading conveys orindicates any preference or requirement for particular materials,material properties, element proportions, element dimensions,commonalities of similarly illustrated elements, or any othercharacteristic, attribute, or property for any element illustrated inthe accompanying figures.

Additionally, it should be understood that the proportions anddimensions (either relative or absolute) of the various features andelements (and collections and groupings thereof) and the boundaries,separations, and positional relationships presented therebetween, areprovided in the accompanying figures merely to facilitate anunderstanding of the various embodiments described herein and,accordingly, may not necessarily be presented or illustrated to scale,and are not intended to indicate any preference or requirement for anillustrated embodiment to the exclusion of embodiments described withreference thereto.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following description is not intended to limit the embodiments toone preferred embodiment. To the contrary, it is intended to coveralternatives, modifications, and equivalents as can be included withinthe spirit and scope of the described embodiments as defined by theappended claims.

One type of optical sensor that may be improved when it is configured tosense different electromagnetic radiation wavelengths is the ambientlight sensor (ALS). However, the area within a device that is allocatedfor implementing an ALS may be relatively small, and it may bebeneficial to reduce the area allocated for implementing an ALS evenfurther and/or provide more ALS functionality within the allotted area.When an electrically-tunable optical filter is positioned in the opticalreception path of an ALS pixel, a single ALS pixel may be used to sensedifferent electromagnetic radiation wavelengths (or different ranges ofelectromagnetic radiation wavelengths) at different times (e.g., thesensing of different electromagnetic radiation wavelengths may betime-modulated). The different electromagnetic radiation wavelengths (orranges of wavelengths) may include different visible and/or non-visibleelectromagnetic radiation wavelengths. An ALS that includes a couple ora few pixels, one or more of which receive electromagnetic radiationthrough a respective electrically-tunable optical filter, may sense evenmore different electromagnetic radiation wavelengths (or more differentranges of electromagnetic radiation wavelengths) or may sense differentelectromagnetic radiation wavelengths (or ranges of wavelengths)quicker.

In some cases, the intensities of the different electromagneticradiation wavelengths sensed by an ALS may be used to adjust thebrightness or color (e.g., white point) of a display, so that thedisplay may be viewed more easily in a particular ambient light. Theintensities of the different electromagnetic radiation wavelengthssensed by an ALS may also be used to conserve power, such as byoperating a display at no more than a needed brightness for a particularambient light condition.

These and other aspects are described with reference to FIGS. 1-8 .However, those skilled in the art will readily appreciate that thedetailed description given herein with respect to these figures is forexplanatory purposes only and should not be construed as limiting.

Directional terminology, such as “top”, “bottom”, “upper”, “lower”,“front”, “back”, “over”, “under”, “above”, “below”, “left”, “right”,etc. is used with reference to the orientation of some of the componentsin some of the figures described below. Because components in variousembodiments can be positioned in a number of different orientations,directional terminology is used for purposes of defining relativepositions of various structures, and may not always define absolutepositions. For example, a first structure described as being “above” asecond structure and “below” a third structure is also “between” thesecond and third structures, and would be “above” the third structureand “below” the second structure if the stack of structures were to beflipped. Also, as used herein, the phrase “at least one of” preceding aseries of items, with the term “and” or “or” to separate any of theitems, modifies the list as a whole, rather than each member of thelist. The phrase “at least one of” does not require selection of atleast one of each item listed; rather, the phrase allows a meaning thatincludes one or more of any of the items, or one or more of anycombination of the items, or one or more of each of the items. By way ofexample, the phrases “at least one of A, B, and C” or “at least one ofA, B, or C” each refer to one or more of only A, only B, or only C; anycombination of A, B, or C; and one or more of each of A, B, and C.Similarly, it may be appreciated that an order of elements presented fora conjunctive or disjunctive list provided herein should not beconstrued as limiting the disclosure to only that order provided.

As used herein, a “layer” refers to one or more materials that aretypically, but not necessarily, parallel to the top surface and/orbottom surface of a substrate or another layer.

FIG. 1 shows an isometric view of a first example optoelectronic device100. By way of example, the device 100 may be configured as an opticalsensor, an optical emitter, or an optical transceiver including both anoptical sensor and an optical emitter. As an optical sensor, the device100 may be used as an ambient light sensor, a proximity sensor, and soon. As an optical emitter, the device 100 may be used as a flood or spotilluminator for example. As an optical transceiver, the device 100 mayperform the functions of both a photodetector and an optical emitter.

When the device 100 is configured as an optical sensor, the device 100may include a photodetector 102 (e.g., a photodiode or phototransistor)and a metasurface 104 defining part or all of an optical stack 106(e.g., an optical sensor stack). The metasurface 104 may be disposedover a light-receiving surface 108 of the photodetector 102 and includea layer 110 having an electrically-tunable optical property (e.g., atunable refractive index). A controller 112 may be configured to applyan electrical bias to the metasurface 104. For example, the controller112 may be configured to program a voltage source 114 coupled to themetasurface 104, which voltage source 114 is configured to apply avoltage to the metasurface 104 (e.g., via interconnect 116 including oneor more conductive vias, conductive traces, wires, and so on). In somecases, the controller 112 may be configured to program the voltagesource 114 in different ways, to apply different voltages to themetasurface 104. In some cases, the controller 112 may program thevoltage source 114 to provide a neutral voltage to the metasurface 104,or may cause the metasurface 104 to be grounded, or may turn the voltagesource 114 off, thereby allowing the metasurface 104 to assume anunbiased state.

When a first electrical bias (e.g., a first voltage) is applied to themetasurface 104, the electrically-tunable optical property of the layer110 may be tuned to a first state, consequently changing anelectrically-tunable optical filtering property of the metasurface 104to a first state. When a second electrical bias (e.g., a second voltage)is applied to the metasurface 104, the electrically-tunable opticalproperty of the metasurface 104 may be tuned to a second state,different from the first state, changing the electrically-tunableoptical filtering property of the metasurface 104 to a second state, andso on. In some cases, the controller 112 may be configured to apply anynumber of one or more different electrical biases to the metasurface104, with different electrical biases tuning the electrically-tunableoptical property of the layer 110 to different states, and also tuningthe electrically-tunable optical filtering property of the metasurface104 to different states.

In some embodiments, the electrically-tunable optical filtering propertyof the metasurface 104 may be an optical passband peak. Thus, when theelectrically-tunable optical filtering property is in the first state,the metasurface 104 may have a first optical passband peak and, when theelectrically-tunable optical filtering property is in the second state,the metasurface 104 may have a second optical passband peak, differentfrom the first optical passband peak. In some cases, the first andsecond states may have first and second optical passband peaks atdifferent visible electromagnetic radiation wavelengths (e.g., green,yellow, red, blue, and so on). In other cases, the first state of theelectrically-tunable optical filtering property may be associated with afirst optical passband peak at a visible electromagnetic radiationwavelength, and the second state of the electrically-tunable opticalfiltering property may be associated with a second optical passband peakat a near-infrared electromagnetic radiation wavelength. The first andsecond states may alternatively have respective optical passband peaksat different non-visible electromagnetic radiation wavelengths (e.g.,infrared (IR), near-IR, or ultraviolet (UV) wavelengths) or, moregenerally, at any two different electromagnetic radiation wavelengths.In this manner, the metasurface 104 may function as anelectrically-tunable optical filter (i.e., an electrically-tunableelectromagnetic radiation filter), such as a tunable color filter.Alternatively, the electrically-tunable optical filtering property maybe an optical passband width (or range of electromagnetic radiationwavelengths) or another property.

By tuning the electrically-tunable optical property of the layer 110,different wavelengths of electromagnetic radiation may be allowed topass through the metasurface 104 to the photodetector 102, such that thepassed electromagnetic radiation wavelengths may be detected and/ormeasured.

When the device 100 is configured as an optical emitter, the device 100may include a light-emitting element 102 (e.g., a light-emitting diode(LED)) and a metasurface 104 defining part or all of an optical stack106 (e.g., an optical emitter stack). The light-emitting element 102 mayemit a range of electromagnetic radiation wavelengths, and in some casesmay include a set of sub-pixels, with each sub-pixel emitting the sameor different ranges of electromagnetic radiation wavelengths. Themetasurface 104 may be disposed over an emission surface 108 of thelight-emitting element 102 and include a layer 110 having anelectrically-tunable optical property (e.g., a tunable refractiveindex). A controller 112 may be configured to apply an electrical biasto the metasurface 104. For example, the controller 112 may beconfigured to program a voltage source 114 coupled to the metasurface104, which voltage source 114 applies a voltage to the metasurface 104.The metasurface 104, controller 112, and voltage source 114 may all beconfigured and operated similarly to how they are configured andoperated when the device 100 is configured as an optical sensor, toallow different wavelengths of electromagnetic radiation emitted by thelight-emitting element 102 to pass through the metasurface 104.

When the device 100 is configured as an optical transceiver, the device100 may both sense and emit through the metasurface 104.

FIG. 2 shows an isometric view of a second example optoelectronic device200. The device 200 includes an array of pixels 202. By way of example,the pixels 202 in the array of pixels 202 are shown to be arranged in mcolumns and n rows (i.e., in an m×n array of pixels 202, where m and nare the same or different integers). However, the pixels 202 mayalternatively be arranged in a single column or row, in concentriccircles, or in other ways.

The device 200 may be configured as an optical sensor or an opticalemitter, or may include a subset of optical sensor pixels co-locatedwith, or interspersed with, a subset of optical emitter pixels. Eachoptical sensor pixel in the array of pixels 202 (or one or multipleoptical sensor pixels) may be configured similarly to the optoelectronicdevice described with reference to FIG. 1 when the device is configuredas an optical sensor. Each optical emitter pixel in the array of pixels202 (or one or multiple optical emitter pixels) may be configuredsimilarly to the optoelectronic device described with reference to FIG.1 when the device is configured as an optical emitter. The device 200 asa whole, or those pixels 202 that are configured to operate as anoptical sensor, may be used as an ambient light sensor, a proximitysensor, a light emitting element white point or health sensor, and soon. The device 200 as a whole, or those pixels 202 that are configuredto operate as an optical emitter, may be used as a flood or spotilluminator, a display, and so on.

In some cases, a respective voltage source 114 may be electricallycoupled to the metasurface 104 of each pixel 202 (e.g., in a one-to-onerelationship), such that each voltage source 114 may apply a voltage toa respective metasurface 104 of a respective pixel 202. In otherembodiments, a single voltage source (e.g., a voltage source havingmultiple taps) may be coupled to a subset or all of the pixels 202. Ineither case, a controller 204 may be configured to program therespective voltage sources 114 (or program a singular or fewer number ofvoltage sources having multiple taps or outputs).

The controller 204 may program the voltage source(s) 114 that areelectrically coupled to first and second pixels 202 such that a samevoltage is applied to the first and second pixels 202 at a same time ordifferent times, or such that a first voltage is applied to the firstpixel 202 and a second voltage, different from the first voltage, isapplied to the second pixel 202 (at a same time or different times).

FIGS. 3A-3C show an example pixel 300 of an optoelectronic device. FIG.3A shows an elevation of the pixel 300; FIG. 3B shows a plan view of anexample array of conductive nanostructures included in the pixel 300;and FIG. 3C shows an isometric view of an example conductivenanostructure included in the array of conductive nanostructures. Insome embodiments, the pixel 300 may be the optoelectronic devicedescribed with reference to FIG. 1 . In some embodiments, the pixel 300may be a pixel of the optoelectronic device described with reference toFIG. 2 (and in some cases, each optical sensor pixel (or multipleoptical sensor pixels) in the optoelectronic device described withreference to FIG. 2 may be configured the same as, or similarly to, thepixel 300).

As shown in FIG. 3A, the pixel 300 may include a photodetector 302(e.g., a photodiode or a phototransistor). Alternatively, thephotodetector 302 may be replaced with a light-emitting element, or withboth a photodetector and a light-emitting element.

A metasurface 304 may be disposed over a light-receiving surface 306 ofthe photodetector 302. The metasurface 304 may include a firstconductive layer 308 having an electrically-tunable optical property(e.g., a tunable refractive index), and an array of conductivenanostructures 310 disposed on a first side of the first conductivelayer 308. In some cases, the first conductive layer 308 may includeindium tin oxide (ITO). The first conductive layer 308 may also oralternatively include boron nitride (BN), silicon (Si), atwo-dimensional (2D) material (e.g., hexagonal BN (h-BN), graphene, ormolybdenum disulfide (MoS₂)), a semiconductor material, and so on. Insome cases, the first conductive layer 308 may be doped or treated tochange its charge carrier concentration. The array of conductivenanostructures 310 may include an array of nanowires, nanocrosses,nanoprisms, or other nanostructures. The conductive nanostructures 310may include one or more of gold (Au), silver (Ag), aluminum (Al), orother conductive materials.

The pixel 300 may include a second conductive layer 312 on a second sideof the first conductive layer. The second conductive layer 312 may be acontinuous layer of conductive material, or the second conductive layer312 may include an array of conductive structures (e.g., a second arrayof conductive nanostructures). In some cases, the second conductivelayer 312 may include one or more of gold, silver, aluminum, or otherconductive materials.

The pixel 300 may further include an electrical insulator 314 disposedbetween the first conductive layer 308 and the second conductive layer312. The electrical insulator 314 may be a continuous layer ofelectrically insulating material, or may include an array ofelectrically insulating structures. In some cases, the electricalinsulator 314 may include alumina (Al₂O₃).

Optionally, a silicon nitride (Si₃N₄) layer 316 may be positionedbetween the photodetector 302 and the second conductive layer 312, withthe second conductive layer 312 being disposed on the silicon nitridelayer 316.

The metasurface 304, electrical insulator 314, and second conductivelayer 312 form a metal-insulator-metal junction. Applying an externalvoltage across the junction may cause free charge carriers to beredistributed in the first conductive layer 308, which may alter bothits electrical properties (e.g., carrier concentration) and opticalproperties (e.g., refractive index). While the array of conductivenanostructures 310 may be engineered to provide a default narrow-bandtransmission/reflection filtering peak (i.e., an optical passband peak)for the metasurface 304, by means of the chosen geometrical propertiesfor the array of conductive nanostructures 310, the narrow-bandtransmission/reflection filtering peak may be tuned to different peaksby applying different external voltages to the metasurface 304.

An external voltage may be applied by a voltage source 318 that iselectrically connected to the metasurface 304 and the second conductivelayer 312 and, in some cases, may be connected to the array ofconductive nanostructures 310 and the second conductive layer 312.

A controller 320 may be used to change the electrical bias (e.g.,voltage, V_(g)) of the metasurface 304. For example, the controller 320may be coupled to the voltage source 318 and may change the voltageapplied to the metasurface 304 by programming the voltage source 318.More specifically, the controller 320 may program the voltage source 318to tune or change a voltage between the metasurface 304 and the secondconductive layer 312, or between the array of conductive nanostructures310 and the second conductive layer 312, or between the first conductivelayer 308 and the second conductive layer 312.

Changing the electrical bias (e.g., voltage) of the metasurface 304 maytune the state of the electrically-tunable optical property of the firstconductive layer 308. In some cases, the controller 320 may cause afirst voltage, a second voltage, and so on to be applied to themetasurface 304. At each voltage, the electrically-tunable opticalproperty of the first conductive layer 308 may assume a different state.The different states may result from different carrier concentrations ofthe first conductive layer 308. In some cases, one of the voltages (orother electrical biases) may be a neutral voltage, ground, orsteady-state voltage of the metasurface 304 when the voltage source 318is disconnected from the metasurface 304 or in an off state (e.g., atzero volts (V)).

The state of the electrically-tunable optical property of the firstconductive layer 308 may influence or determine a corresponding state ofan electrically-tunable optical filtering property of the metasurface304. When the electrically-tunable optical filtering property of themetasurface 304 is an optical passband peak, a first state of theelectrically-tunable optical filtering property may be associated with afirst optical passband peak at a first electromagnetic radiationwavelength. A second state of the electrically-tunable optical filteringproperty may be associated with a second optical passband peak at asecond electromagnetic radiation wavelength. This enables themetasurface 304 to operate as an electrically-tunable optical filter(i.e., an electrically-tunable electromagnetic radiation filter), suchas a tunable color filter. In some cases, both the first and secondoptical passband peaks may be at different visible electromagneticradiation wavelengths (e.g., green, yellow, red, blue, and so on), or atdifferent non-visible electromagnetic radiation wavelengths (e.g., atone or more IR, near-IR, or UV electromagnetic radiation wavelengths),or at respective visible and non-visible electromagnetic radiationwavelengths.

In some embodiments of the pixel 300, the first conductive layer 308 maybe formed of or include ITO; the array of conductive nanostructures 310may be or include an array of gold nanowires; the second conductivelayer 312 may be formed of or include gold; the electrical insulator 314may be formed of or include alumina; and the second conductive layer 312may be disposed on a silicon nitride layer 316.

FIG. 3B shows a plan view of an example array of conductivenanostructures 310 included in the pixel 300. In FIG. 3B, eachconductive nanostructure 310 is shown to be a nanowire having a width(W) and a length (L). By way of example, each conductive nanostructure310 is shown to have a square or rectangular block-like shape, withdifferent conductive nanostructures 310 having a periodicity of P_(x) inan x-direction of a Cartesian coordinate system, and a periodicity ofP_(y) in a y-direction of the Cartesian coordinate system. Theseparation between conductive nanostructures is S_(x) in the x-direction(S_(x)=P_(x)−W) and S_(y) in the y-direction (S_(y)=P_(y)−L).

FIG. 3C shows a perspective view of an example conductive nanostructure310 included in the array of conductive nanostructures 310. As shown,the conductive nanostructure 310 may have a block-like shape, with awidth (W), length (L), and height (H).

When constructing the pixel 300, the parameters W, L, H, Px, Py, Sx, andSy may all be adjusted to set a default optical passband peak for themetasurface 304. The default optical passband peak is an opticalpassband peak (or state) that exists when the metasurface 304 is biasedto a neutral voltage, ground, or steady-state voltage that may existwhen the voltage source 318 is disconnected from the metasurface 304 orin an off state (e.g., at zero volts (V)).

FIG. 3D shows an alternative view of the layers circumscribed by thebubble IIID in FIG. 3A. As shown in FIG. 3D, the conductivenanostructures 310 may have different sizes or shapes, depending onwhere they are located. For example, one or more conductivenanostructures 310-1 near one or more peripheral portions of the pixel300 may have larger widths or lengths (or even a larger height), and maybe designed for connection (bonding) of a wire or conductive trace thatconnects the array of conductive nanostructures 310 to the voltagesource 318. One or more conductive nanostructures 310-2 positioned moreinterior to the pixel 300 may have smaller widths or lengths (and evensmaller heights), and may be designed specifically to tune the opticalcharacteristics of the array of conductive nanostructures 310.

As also shown in FIG. 3D, the second conductive layer 312, and in somecases the first conductive layer 308 and the insulator 314, may bethinned. Thinning these layers can improve their transmissivity, reducethe height of the pixel 300, reduce materials cost, and so on. In someembodiments, peripheral portions of the second conductive layer 312 maybe made thicker than an interior portion of the second conductive layer312, to provide a more substantial conductive pad for connection(bonding) of a wire or conductive trace that connects the secondconductive layer 312 to the voltage source 318.

FIG. 4 shows a graph 400 of the different optical responses that may beprovided by a metasurface tuned to different representative states. Asan example, the metasurface may be the metasurface described withreference to any of FIGS. 1-3C. The horizontal axis of the graph 400shows a range of example electromagnetic radiation wavelengths. Thevertical axis shows a percentage transmission (e.g., 0.7=70%) ofelectromagnetic radiation through a metasurface.

The graphed waveforms (402, 404, 406, and so on) show the opticalpassband and optical passband peak of the metasurface when it iselectrically biased to various voltages.

FIGS. 5A and 5B show a first example of an electronic device 500. Thedevice's dimensions and form factor, including the ratio of the lengthof its long sides to the length of its short sides, suggest that thedevice 500 is a mobile phone (e.g., a smartphone). However, the device'sdimensions and form factor are arbitrarily chosen, and the device 500could alternatively be any portable electronic device including, forexample, a mobile phone, tablet computer, portable computer, portablemusic player, health monitor device, portable terminal, vehiclenavigation system, robot navigation system, wearable device (e.g., ahead-mounted display (HMD), glasses, watch, earphone or earbud, and soon), or other portable or mobile device. The device 500 could also be adevice that is semi-permanently located (or installed) at a singlelocation. FIG. 5A shows a front isometric view of the device 500, andFIG. 5B shows a rear isometric view of the device 500. The device 500may include a housing 502 that at least partially surrounds a display504. The housing 502 may include or support a front cover 506 or a rearcover 508. The front cover 506 may be positioned over the display 504,and may provide a window through which the display 504 may be viewed. Insome embodiments, the display 504 may be attached to (or abut) thehousing 502 and/or the front cover 506. In alternative embodiments ofthe device 500, the display 504 may not be included and/or the housing502 may have an alternative configuration.

The display 504 may include one or more light-emitting elements and maybe configured, for example, as an LED display, an organic LED (OLED)display, a liquid crystal display (LCD), an electroluminescent (EL)display, or other type of display. In some embodiments, the display 504may include, or be associated with, one or more touch and/or forcesensors that are configured to detect a touch and/or a force applied toa surface of the front cover 506.

The various components of the housing 502 may be formed from the same ordifferent materials. For example, a sidewall 518 of the housing 502 maybe formed using one or more metals (e.g., stainless steel), polymers(e.g., plastics), ceramics, or composites (e.g., carbon fiber). In somecases, the sidewall 518 may be a multi-segment sidewall including a setof antennas. The antennas may form structural components of the sidewall518. The antennas may be structurally coupled (to one another or toother components) and electrically isolated (from each other or fromother components) by one or more non-conductive segments of the sidewall518. The front cover 506 may be formed, for example, using one or moreof glass, a crystal (e.g., sapphire), or a transparent polymer (e.g.,plastic) that enables a user to view the display 504 through the frontcover 506. In some cases, a portion of the front cover 506 (e.g., aperimeter portion of the front cover 506) may be coated with an opaqueink to obscure components included within the housing 502. The rearcover 508 may be formed using the same material(s) that are used to formthe sidewall 518 or the front cover 506. In some cases, the rear cover508 may be part of a monolithic element that also forms the sidewall 518(or in cases where the sidewall 518 is a multi-segment sidewall, thoseportions of the sidewall 518 that are non-conductive). In still otherembodiments, all of the exterior components of the housing 502 may beformed from a transparent material, and components within the device 500may or may not be obscured by an opaque ink or opaque structure withinthe housing 502.

The front cover 506 may be mounted to the sidewall 518 to cover anopening defined by the sidewall 518 (i.e., an opening into an interiorvolume in which various electronic components of the device 500,including the display 504, may be positioned). The front cover 506 maybe mounted to the sidewall 518 using fasteners, adhesives, seals,gaskets, or other components.

A display stack or device stack (hereafter referred to as a “stack”)including the display 504 may be attached (or abutted) to an interiorsurface of the front cover 506 and extend into the interior volume ofthe device 500. In some cases, the stack may include a touch sensor(e.g., a grid of capacitive, resistive, strain-based, ultrasonic, orother type of touch sensing elements), or other layers of optical,mechanical, electrical, or other types of components. In some cases, thetouch sensor (or part of a touch sensor system) may be configured todetect a touch applied to an outer surface of the front cover 506 (e.g.,to a display surface of the device 500).

In some cases, a force sensor (or part of a force sensor system) may bepositioned within the interior volume below and/or to the side of thedisplay 504 (and in some cases within the device stack). The forcesensor (or force sensor system) may be triggered in response to thetouch sensor detecting one or more touches on the front cover 506 (or alocation or locations of one or more touches on the front cover 506),and may determine an amount of force associated with each touch, or anamount of force associated with the collection of touches as a whole.Alternatively, the force sensor (or force sensor system) may triggeroperation of the touch sensor (or touch sensor system) in response todetecting a force on the front cover 506. In some cases, the forcesensor (or force sensor system) may be used to determine the locationsof touches on the front cover 506, and may thereby function as a touchsensor (or touch sensor system).

As shown primarily in FIG. 5A, the device 500 may include various othercomponents. For example, the front of the device 500 may include one ormore front-facing cameras 510, speakers 512, microphones, or othercomponents 514 (e.g., audio, imaging, sensing components, and/or lightsources) that are configured to transmit or receive signals to/from thedevice 500. In some cases, a front-facing camera 510, alone or incombination with other sensors, may be configured to operate as abio-authentication or facial recognition sensor. The device 500 may alsoinclude various input and/or output devices 516, which may be accessiblefrom the front surface (or display surface) of the device 500. In somecases, the front-facing camera 510, I/O devices 516, and/or othersensors of the device 500 may be integrated with a display stack of thedisplay 504 and moved under the display 504.

In some cases, one or more of the camera 510, components 514, and/or I/Odevices 516 may include one or an array of optical sensors or opticalsensor pixels, some or all of which may be configured as described inthe present disclosure. The optical sensors or optical sensor pixels maybe used, for example, as one or more ambient light sensors, proximitysensors, touch sensors, biometric sensors, time-of-flight sensors, depthsensors, optical signal receivers, and so on. In some cases, one or moreof the display 504 and/or components 514 may include one or an array ofoptical emitters or optical emitter pixels, some or all of which may beconfigured as described in the present disclosure. The optical emittersor optical emitter pixels may be used, for example, as one or moredisplay elements (e.g., display pixels), illuminators, optical signaltransmitters, and so on. Each of the optical sensors, optical sensorpixels, optical emitters, and/or optical emitter pixels may beconfigured to receive or emit different electromagnetic radiationwavelengths at different times, by electrically tuning an opticalproperty of a layer of a metasurface of the respective sensor, emitter,or pixel.

The device 500 may also include buttons or other input devicespositioned along the sidewall 518 and/or on a rear surface of the device500. For example, a volume button or multipurpose button 520 may bepositioned along the sidewall 518, and in some cases may extend throughan aperture in the sidewall 518. The sidewall 518 may include one ormore ports 522 that allow air, but not liquids, to flow into and out ofthe device 500. In some embodiments, one or more sensors may bepositioned in or near the port(s) 522. For example, an ambient lightsensor or other optical sensor, ambient pressure sensor, ambienttemperature sensor, internal/external differential pressure sensor, gassensor, particulate matter sensor, or air quality sensor may bepositioned in or near a port 522. In some cases, one or more sensorspositioned near a port 522 may be an optical sensor as described herein.

In some embodiments, the rear surface of the device 500 may include arear-facing camera 524 or other optical sensor or optical sensorpixel(s) (see FIG. 5B). A flash or light source 526 (e.g., an opticalemitter or optical emitter pixel) may also be positioned along the rearof the device 500 (e.g., near the rear-facing camera). In some cases,the rear surface of the device 500 may include multiple rear-facingcameras.

The camera(s), microphone(s), pressure sensor(s), temperature sensor(s),biometric sensor(s), button(s), proximity sensor(s), touch sensor(s),force sensor(s), particulate matter or air quality sensor(s), opticalsensor(s), and so on of the device 500 may form parts of various sensorsystems.

FIGS. 6A and 6B show a second example of an electronic device 600. Thedevice's dimensions and form factor, and inclusion of a band 604,suggest that the device 600 is an electronic watch. However, the device600 could alternatively be any wearable electronic device. FIG. 6A showsa front isometric view of the device 600, and FIG. 6B shows a rearisometric view of the device 600. The device 600 may include a body 602(e.g., a watch body) and a band 604. The watch body 602 may include aninput or selection device, such as a crown 614 or a button 616. The band604 may be used to attach the body 602 to a body part (e.g., an arm,wrist, leg, ankle, or waist) of a user. The body 602 may include ahousing 606 that at least partially surrounds a display 608. The housing606 may include or support a front cover 610 (FIG. 6A) or a rear cover612 (FIG. 6B). The front cover 610 may be positioned over the display608, and may provide a window through which the display 608 may beviewed. In some embodiments, the display 608 may be attached to (orabut) the housing 606 and/or the front cover 610. In alternativeembodiments of the device 600, the display 608 may not be includedand/or the housing 606 may have an alternative configuration.

The housing 606 may in some cases be similar to the housing describedwith reference to FIGS. 5A and 5B, and the display 608 may in some casesbe similar to the display described with reference to FIGS. 5A-5B.

The device 600 may include various sensor systems, and in someembodiments may include some or all of the sensor systems included inthe device described with reference to FIGS. 5A-5B. In some embodiments,the device 600 may have a port 618 (or set of ports) on a side of thehousing 606 (or elsewhere), and an ambient light sensor or other opticalsensor, ambient pressure sensor, ambient temperature sensor,internal/external differential pressure sensor, gas sensor, particulatematter sensor, or air quality sensor may be positioned in or near theport(s) 618. In some cases, one or more sensors positioned near a port618 may be an optical sensor as described herein.

In some cases, the rear surface (or skin-facing surface) of the device600 may include a flat or raised area 620 that includes one or moreskin-facing sensors. For example, the area 620 may include a heart-ratemonitor, a respiration-rate monitor, or a blood pressure monitor. Thearea 620 may also include an off-wrist detector or other sensor. In somecases, one or more of the skin-facing sensors may be an optical sensoras described herein.

In some cases, one or more cameras, sensors, light sources, or I/Odevices of the device 600 (including optical sensors in its body 602,band 604, or band attachment mechanism) may include one or more opticalsensors, optical sensor pixels, optical emitters, or optical emitterpixels, some or all of which may be configured as described in thepresent disclosure. The optical sensors or optical sensor pixels may beused, for example, as one or more ambient light sensors, proximitysensors, touch sensors, biometric sensors, time-of-flight sensors, depthsensors, optical signal receivers, and so on. The optical emitters oroptical emitter pixels may be used, for example, as one or more displayelements (e.g., display pixels), illuminators, optical signaltransmitters, and so on. Each of the optical sensors, optical sensorpixels, optical emitters, and/or optical emitter pixels may beconfigured to receive or emit different electromagnetic radiationwavelengths at different times, by electrically tuning an opticalproperty of a layer of a metasurface of the respective sensor, emitter,or pixel.

FIG. 7 shows a sample electrical block diagram of an electronic device700, which electronic device may in some cases take the form of thedevice described with reference to FIGS. 5A-5B or FIGS. 6A-6B and/orinclude the optical sensor, optical emitter, pixel, or array of pixelsdescribed with reference to any of FIGS. 1-3C and 5A-6B. The electronicdevice 700 may include a display 702 (e.g., a light-emitting display), aprocessor 704, a power source 706, a memory 708 or storage device, asensor system 710, or an input/output (I/O) mechanism 712 (e.g., aninput/output device, input/output port, or haptic input/outputinterface). The processor 704 may control some or all of the operationsof the electronic device 700. The processor 704 may communicate, eitherdirectly or indirectly, with some or all of the other components of theelectronic device 700. For example, a system bus or other communicationmechanism 714 can provide communication between the display 702, theprocessor 704, the power source 706, the memory 708, the sensor system710, and the I/O mechanism 712.

The processor 704 may be implemented as any electronic device capable ofprocessing, receiving, or transmitting data or instructions, whethersuch data or instructions is in the form of software or firmware orotherwise encoded. For example, the processor 704 may include amicroprocessor, a central processing unit (CPU), an application-specificintegrated circuit (ASIC), a digital signal processor (DSP), acontroller, or a combination of such devices. As described herein, theterm “processor” is meant to encompass a single processor or processingunit, multiple processors, multiple processing units, or other suitablyconfigured computing element or elements.

It should be noted that the components of the electronic device 700 canbe controlled by multiple processors. For example, select components ofthe electronic device 700 (e.g., the sensor system 710) may becontrolled by a first processor and other components of the electronicdevice 700 (e.g., the display 702) may be controlled by a secondprocessor, where the first and second processors may or may not be incommunication with each other.

The power source 706 can be implemented with any device capable ofproviding energy to the electronic device 700. For example, the powersource 706 may include one or more batteries or rechargeable batteries.Additionally or alternatively, the power source 706 may include a powerconnector or power cord that connects the electronic device 700 toanother power source, such as a wall outlet.

The memory 708 may store electronic data that can be used by theelectronic device 700. For example, the memory 708 may store electricaldata or content such as, for example, audio and video files, documentsand applications, device settings and user preferences, timing signals,control signals, and data structures or databases. The memory 708 mayinclude any type of memory. By way of example only, the memory 708 mayinclude random access memory, read-only memory, Flash memory, removablememory, other types of storage elements, or combinations of such memorytypes.

The electronic device 700 may also include one or more sensor systems710 positioned almost anywhere on the electronic device 700. In somecases, sensor systems 710 may be positioned as described with referenceto FIGS. 5A-5B or FIGS. 6A-6B. The sensor system(s) 710 may beconfigured to sense one or more type of parameters, such as, but notlimited to, electromagnetic radiation (light); touch; force; heat;movement; relative motion; biometric data (e.g., biological parameters)of a user; particulate matter concentration, air quality; proximity;position; connectedness; and so on. By way of example, the sensorsystem(s) 710 may include a heat sensor, a position sensor, a light oroptical sensor (e.g., an ambient light sensor or proximity sensor), anaccelerometer, a pressure transducer, a gyroscope, a magnetometer, ahealth monitoring sensor, a particulate matter sensor, an air qualitysensor, and so on. Additionally, the one or more sensor systems 710 mayutilize any suitable sensing technology, including, but not limited to,magnetic, capacitive, ultrasonic, resistive, optical, acoustic,piezoelectric, or thermal technologies.

The I/O mechanism 712 may transmit or receive data from a user oranother electronic device. The I/O mechanism 712 may include the display702, a touch sensing input surface, a crown, one or more buttons (e.g.,a graphical user interface “home” button), one or more cameras(including an under-display camera), one or more microphones orspeakers, one or more ports such as a microphone port, and/or akeyboard. Additionally or alternatively, the I/O mechanism 712 maytransmit electronic signals via a communications interface, such as awireless, wired, and/or optical communications interface. Examples ofwireless and wired communications interfaces include, but are notlimited to, cellular and Wi-Fi communications interfaces.

FIG. 8 shows an example method 800 of characterizing ambient light. Themethod 800 may be performed, for example, using the optical sensordescribed with reference to FIG. 1, 2, 3A-3D, 5A-5B, 6A-6B, or 7.

At block 802, the method 800 may include receiving a first set ofwavelengths of the ambient light through a metasurface, while themetasurface is in a first state. The metasurface may include an array ofnanowires formed on a layer of material having an electrically-tunableoptical property (e.g., a tunable refractive index). In variousembodiments, the metasurface may be configured similarly to any of themetasurfaces described herein.

At block 804, the method 800 may include measuring a first intensity ofthe first set of wavelengths.

At block 806, the method 800 may include applying a voltage (e.g., afirst voltage) to the metasurface, to bias the metasurface to a secondstate different from the first state.

At block 808, the method 800 may include receiving a second set ofwavelengths of the ambient light through the metasurface, while themetasurface is in the second state.

At block 810, the method 800 may include measuring a second intensity ofthe second set of wavelengths.

At block 812, the method 800 may include characterizing the ambientlight using the first intensity and the second intensity.

Optionally, and at block 814, the method 800 may include applying asecond voltage to the metasurface, to bias the metasurface to the firststate prior to measuring the first intensity of the first set ofwavelengths at block 804.

Optionally, and at block 816, the method 800 may include adjusting asetting of a display responsive to the characterization of the ambientlight.

Optionally, the method 800 may include applying at least one additionalvoltage to the metasurface to bias the metasurface to at least onerespective additional state. In some cases, a respective additional setof wavelengths of ambient light may be received through the metasurfacewhile the metasurface is biased to each of the at least one additionalstate, and the intensity of each additional set of wavelengths may bemeasured. The ambient light may then be characterized using the measuredintensities of any of the sets of wavelengths.

The foregoing description, for purposes of explanation, uses specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art,after reading this description, that the specific details are notrequired in order to practice the described embodiments. Thus, theforegoing descriptions of the specific embodiments described herein arepresented for purposes of illustration and description. They are nottargeted to be exhaustive or to limit the embodiments to the preciseforms disclosed. It will be apparent to one of ordinary skill in theart, after reading this description, that many modifications andvariations are possible in view of the above teachings.

What is claimed is:
 1. An optical device stack, comprising: at least oneof a photodetector or an optical emitter; a metasurface disposed over atleast one of a light-receiving surface of the photodetector or a lightemission surface of the optical emitter and including, a firstconductive layer having an electrically-tunable optical property; and anarray of conductive nanostructures disposed on a first side of the firstconductive layer; a second conductive layer disposed on a second side ofthe first conductive layer; and an electrical insulator disposed betweenthe first conductive layer and the second conductive layer; wherein, achange in an electrical bias between the metasurface and the secondconductive layer, from a first electrical bias to a second electricalbias, tunes the electrically-tunable optical property from a first stateto a second state, and changes an electrically-tunable optical filteringproperty of the metasurface.
 2. The optical device stack of claim 1,wherein the first conductive layer comprises indium tin oxide.
 3. Theoptical device stack of claim 1, wherein the array of conductivenanostructures comprises an array of nanowires.
 4. The optical devicestack of claim 3, wherein the array of nanowires comprises goldnanowires.
 5. The optical device stack of claim 4, wherein the secondconductive layer comprises gold.
 6. The optical device stack of claim 5,wherein the electrical insulator comprises alumina.
 7. The opticaldevice stack of claim 1, further comprising: a silicon nitride layer;wherein, the second conductive layer is disposed on the silicon nitridelayer and is between the silicon nitride layer and the electricalinsulator.
 8. The optical device stack of claim 1, wherein: the firstelectrical bias is zero volts (V); and when the electrically-tunableoptical property is tuned to the first state, the metasurface has anoptical passband peak at a visible electromagnetic radiation wavelength.9. The optical device stack of claim 8, wherein the visibleelectromagnetic radiation wavelength is one of a red electromagneticradiation wavelength, a green electromagnetic radiation wavelength, or ablue electromagnetic radiation wavelength.
 10. The optical device stackof claim 8, wherein: when the electrically-tunable optical property istuned to the second state, the metasurface has an optical passband peakat one of, a different visible electromagnetic radiation wavelength thanwhen the electrically-tunable optical property is tuned to the firststate; or a near-infrared electromagnetic radiation wavelength.
 11. Anoptoelectronic device, comprising: a pixel including, a metasurfaceincluding an array of gold nanowires disposed on a layer of indium tinoxide (ITO); a layer of gold; and a layer of alumina disposed betweenthe metasurface and the layer of gold; a voltage source electricallyconnected to the metasurface and the layer of gold; and a controllerconfigured to change a voltage between the metasurface and the layer ofgold by programming the voltage source.
 12. The optoelectronic device ofclaim 11, further comprising: an array of pixels including the pixel,wherein multiple pixels in the array of pixels each include, arespective metasurface including a respective array of gold nanowiresdisposed on a respective layer of ITO; a respective layer of gold; and arespective layer of alumina disposed between the respective metasurfaceand the respective layer of gold; and a respective voltage sourceelectrically connected to the respective metasurface and the respectivelayer of gold of each pixel in the multiple pixels.
 13. Theoptoelectronic device of claim 12, wherein: the pixel is a first pixel;the multiple pixels include a second pixel; and the controller isconfigured to program respective voltage sources that are electricallyconnected to the first pixel and the second pixel, to apply a samevoltage to the first pixel and to the second pixel at a same time. 14.The optoelectronic device of claim 12, wherein: the pixel is a firstpixel; the multiple pixels include a second pixel; the controller isconfigured to program respective voltage sources that are electricallyconnected to the first pixel and the second pixel, to apply a firstvoltage to the first pixel and a second voltage to the second pixel at asame time; and the first voltage is different from the second voltage.15. The optoelectronic device of claim 12, wherein each pixel of themultiple pixels comprises a respective photodetector positioned toreceive electromagnetic radiation through a respective metasurface. 16.The optoelectronic device of claim 12, wherein each pixel of themultiple pixels comprises a respective optical emitter positioned toemit electromagnetic radiation through a respective metasurface.
 17. Amethod of characterizing ambient light, comprising: receiving a firstset of wavelengths of the ambient light through a metasurface while themetasurface is in a first state, the metasurface comprising an array ofnanowires formed on a layer of material having an electrically-tunableoptical property; measuring a first intensity of the first set ofwavelengths; applying a voltage to the metasurface to bias themetasurface to a second state different from the first state; receivinga second set of wavelengths of the ambient light through the metasurfacewhile the metasurface is in the second state; measuring a secondintensity of the second set of wavelengths; and characterizing theambient light using at least the first intensity and the secondintensity.
 18. The method of claim 17, wherein the layer of materialhaving the electrically tunable optical property comprises indium tinoxide.
 19. The method of claim 17, further comprising: applying at leastone additional voltage to the metasurface to bias the metasurface to atleast one respective additional state.
 20. The method of claim 17,further comprising: adjusting a setting of a display responsive to thecharacterization of the ambient light.